1. Field of the Invention
The present invention relates to an input device for inputting coordinates on a screen and a display device including the same. In particular, the present invention relates to an input device of an electrostatic capacity type that supports input using such an insulator as a plastic pen, and to a display device including the same.
2. Description of the Related Art
A display device including an input device (hereinafter, also referred to as “touch sensor” or “touch panel”) having an on-screen input function of inputting information to a display screen by a touch operation (contact and press operation, hereinafter, simply referred to as “touch”) with a user's finger or the like is used for mobile electronic devices such as a PDA and a mobile terminal, various home electric appliances, a stationary customer guiding terminal such as an automatic reception machine, and the like. As a method for achieving the input device using the touch, there are known a resistance film method of detecting a change in resistance value of a touched portion, an electrostatic capacity method of detecting a change in capacity thereof, an optical sensor method of detecting a change in quantity of light at the portion shielded by the touch, and the like.
The electrostatic capacity method has the following advantages when compared with the resistance film method or the optical sensor method. For example, a transmittance of the resistance film method or the optical sensor method is as low as 80%. On the other hand, a transmittance of the electrostatic capacity method is as high as about 90%, thereby preventing a reduction in displayed image quality. In the resistance film method, a touch position is detected by mechanical contact to the resistance film, thereby leading to possible deterioration or breakage (crack) of the resistance film. On the other hand, in the electrostatic capacity method, there is no mechanical contact such as contact of a detection electrode with another electrode. Thus, the electrostatic capacity method is advantageous in durability.
An exemplary electrostatic capacity method is disclosed in JP 2003-511799 A (hereinafter, referred to as Patent Document 1). In the method disclosed therein, a vertical detection electrode (x electrode) and a horizontal detection electrode (Y electrode) are arranged in vertical and horizontal two-dimensional matrix, and a capacity of each electrode is detected by an input processing unit. When a conductor such as a finger touches a surface of the touch panel, the capacity of each electrode increases. Thus, the input processing unit detects the touch to calculate input coordinates based on a signal of a capacity change detected by each electrode. Even when the detection electrode is deteriorated to change its resistance value as physical characteristics, such an influence on capacity detection is limited. Thus, there is only a little influence on input position detection accuracy of the touch panel. As a result, high input position detection accuracy may be realized.
In addition, JP 2004-5672 A describes a method of forming a high polymer layer containing conductive fine particles on a surface of a transparent electrode of a touch panel, thereby obtaining a superior antireflection effect and improving transparency.